My problem is that Mixed sweepers tend to need to stick with either Life Orb, which handicaps their durability, or Expert Belt, which just lacks oomph. Noir and Cress wall them pretty easily even without splitting EVs, and Burn + Life Orb is serious damage without you even doing anything, moreso if you had Stealth Rock up.
Oh, and whenever I switch in my big physical attackers in on Blissey or Cress, I tend to get paralysed. Know how useful a paralysed sweeper is? Not very.
Try Electrivire. >_>